1. Field of the Invention
The invention relates generally to power supply systems, and in particular to a battery management system in a mobile communication device.
2. Description of the Related Art
A typical mobile communication device is powered by a rechargeable battery. However, the same mobile communication device may also include several subsystem circuits, such as input/output (I/O) circuits, wireless communication circuits, processing circuits, and the like, to support such device functions as voice communication functions and data communication functions.
Each device function may be supported by one or more subsystem circuits. The activity period of a subsystem circuit varies according to the function activated at the mobile communication device. Thus, power requirements may vary significantly among device functions, due to differences among the subsystem circuits supporting each function and the activity periods of each subsystem circuit. If battery charge is low, the mobile communication device may be able to support lower power functions, but unable to support higher power functions.
Given their larger current requirements, higher power functions discharge a battery more quickly than lower power functions, and may therefore discharge the battery to such a low level that neither higher power functions nor lower power functions may be used. Battery discharge rates are also affected by temperature, such that a battery often discharges more quickly at lower temperatures, during cold weather conditions for example. Although surface charge of a battery may initially support some lower power functions, thereby to reduce cold battery discharge at low temperatures, power requirements for higher power functions are not significantly reduced by surface charge. As such, lower power functions may be preferred over higher power functions when a battery is at a low temperature.
Known power management systems for mobile communication devices typically provide visual or aural indicators that a battery charge is low. Other power management systems reserve battery charge for a one-time operation of a function, such as an emergency 911 call, when the battery charge is low. Still other power management systems provide various power modes dependent upon battery charge level.